Ion transport across the plasma membrane is critical for maintaining the normal physiology of the cell. Ion transport across the plasma membrane is mediated by a variety of membrane bound proteins which act as channels and pumps. Dysfunctional ion channels or pumps will lead to a disease state. Cystic fibrosis is a disease resulting from a defect in a cAMP-mediated chloride channel, CFTR (Welsh et al. 1993, Cell 73:1251). The physiological manifestation of cystic fibrosis includes airway obstruction resulting from thick secretions of mucus into the airways of the lung and gastrointestinal tract and the subsequent colonization of the lung airways by pathogenic microorganisms (Clarke et al. 1992, Science 257:1125; Clarke et al. 1994, Proc Natl Acad Sci USA 91:479; Eng et al. 1996, Ped Pulmonol 21:77) and mucus plugging of pancreatic ducts of the gastrointestinal tract (WO 01/54685). The association of cystic fibrosis with aberrant ion transport has lead investigators to hypothesize that dysfunctional ion transport might be related to other diseases with similar symptoms. Thus, dysfunctional ion transport has been implicated in diseases such as asthma and chronic obstructive pathway disease (COPD), i.e., emphysema and chronic bronchitis.
CLCA1, and its murine homolog, gob-5, are putative calcium activated chloride channels (WO 99/44620). Both have been implicated in the pathology associated with asthma. Asthma is characterized by a hypersensitivity to environmental allergens which is associated with an inflammatory response and the increased production of mucin (WO 01/54685; WO 99/44620). Expression of CLCA1 and gob-5 are up-regulated in response to allergen challenge. Expression has also been linked to mucin overproduction (Hoshino et al. 2002, Am J Respir Crit Care Med 165:1132). Over expression of CLCA1 and gob-5 has been shown to induce expression of MUC5AC, a mucin gene, in a muco-epidermal cell line. Additionally, adenovirus mediated antisense therapy has abrogated the effects of gob-5 hyper-responsiveness and mucin production in an in vivo mouse model (Nakanishi et al. 2001, Proc Natl Acad Sci USA 98:5175).
It has been suggested that CLCA1 is expressed as a 125 kD precursor which is cleaved to form a 90 kD subunit and a 37 kD subunit which associate on the cell surface to form an active ion channel. It has also been suggested that the 90 kD subunit forms four transmembrane domains. It has further been suggested that expression of CLCA1 is associated with chloride ion flux across the plasma membrane and that non-selective chloride channel inhibitors such as niflumic acid, 4,4′-diisothiocyanatostilbene-2,2′-disulfonic acid, and dithiothreitol will abrogate this effect. (Gruber et al. 1999, Genomics 54:200).